Beta V1 release

fix(engine): fill normal-Z gaps after shifted wall removal

When shifted walls are removed from the normal-Z sub-sequence,
consecutive extrusion paths may be left adjacent without a travel
move between them. CuraEngine then extrudes across the gap,
producing spurious green lines in preview.

Phase 3b detects gaps by original-index distance (j > i+1 means
a shifted wall was removed). Two cases handled:
  Case A: extrusion -> gap -> extrusion: synthesize MOVERETRACTED
  Case B: travel -> gap -> extrusion: redirect last travel endpoint

Also adds release profile (strip/LTO/opt-level=z) to Cargo workspaces
for smaller binary output.

Parity changes in engine_prototype.py; test assertions updated to
exclude gap-fill travels (z_offset=0, retract=True) from feature
count checks.